The present disclosure generally relates to an actuator for driving a test element and, in particular, relates to an actuator for driving a test element, wherein the test element comprises a lancet for perforating a skin portion of a living organism.
Monitoring of the concentration of certain analytes in body fluids, such as blood glucose or cholesterol, can form an essential part of the daily routine for many patients suffering from certain diseases, such as diabetes. Thus, in the latter case, the blood glucose level has to be determined several times per day in a fast and reliable way, in order to be able to take appropriate medical measures.
In order to minimize the interruptions of the daily routine of the patient, in many cases, the patient uses mobile analytic systems that are easy to transport and to handle. Thus, for example, the measurement of the blood glucose level may be performed by the patient without leaving his workplace or during his leisure activities.
Many mobile systems are known to a person skilled in the art and are commercially available. These systems may function according to several distinct principles of measurement. Therein, for example, optical and/or electrochemical measurement processes may be used, in order to determine the concentration of the constituent (i.e., the analyte) of the body fluid. Thus, for example, test elements, such as test strips, may be used, which are capable of receiving a sample (e.g., a droplet) of the body fluid to be analyzed. An example of test strips (in this case electrochemical test strips) is given in U.S. Pat. No. 5,286,362. An example of measurement systems using optical analytical methods is given in WO 01/48461. The principles of measurement disclosed in these documents, as well as the chemical substances used therein, may be applied to the present disclosure. Nevertheless, other principles and/or substances may be used.
In most cases, the test elements, which are generally designed to be disposable test elements, can form an important part of the test systems, especially for portable or mobile test systems. Typically, a diabetic uses five to seven test elements per day. In most cases, it can be important to keep the test elements clean and stored under dry conditions in order not to have the measurement affected by ingressing humidity and/or other contaminations. This holds true for test elements such as the test strips mentioned above, as well as for other disposable test elements, such as test elements comprising a lancing system for perforating a skin portion of a living organism, such as of a human patient. For example, WO 03/08834 A1 discloses a device for use with a penetrating member driver to penetrate tissue. The device includes a single disk-shaped cartridge coupled to a plurality of penetrating members and operatively couplable to a penetrating member driver. The penetrating members are movable to extend radially outward from the cartridge to penetrate tissue.
Besides test systems using separate test elements for lancing and for analysis, test systems are known with combined test elements, which are suited for the lancing or sampling action as well as for analysis of the body fluid sample generated by the lancing/sampling action. These test systems, which are commonly known as “get and measure systems” (“GAM-systems”), may be designed as described in WO 2005/084546 A2. In this reference, a body fluid sampling device is disclosed, comprising a skin-piercing element having a collection zone for receiving body fluid, wherein the device further comprises a fluid receiving means remote spaced apart from the collection zone, so that body fluid in the collection zone will not contact the fluid receiving means initially. The collection zone takes up a very small volume of body fluid of about 10 to 500 nanoliters in a very short time period. The fluid receiving means may have a test zone for performing an analytical reaction. Fluid sample from the collection zone is automatically or manually transported to the fluid receiving means to contact the fluid with the test zone.
For sampling the body fluid in GAM-systems, a controlled movement of the skin-piercing or lancing element has been shown to be of some importance. For example, EP 1 709 906 A1 describes a method and a system for sampling of body fluid, wherein a piercing element perforates the skin of a body part in forward movement and collects body fluid using a capillary structure inside the piercing element. The sampling of the body fluid may be optimized by detecting the presence of the body fluid and controlling the penetration depth.
Similarly, WO 2007/045412 A1 describes a test element for use as a disposable article for examining a body fluid comprising a piercing element for piercing a body part, a collection zone configured thereon for body fluid obtained through the puncture and at least one optical waveguide for carrying out an optical measurement in the collection zone. The collection zone is configured by a collecting aperture of the piercing element, which the aperture is elongate in the direction of piercing, and in that the optical waveguide is integrated into the piercing element so as not to be displaced and is arranged with its distal end in a proximal measuring zone of the collecting aperture.
Still, despite of the progress that has been made during the recent years with respect to GAM-systems for piercing a skin portion of a patient and for sampling a body fluid, the precise control of the penetration of the piercing or lancing system remains a major challenge. Thus, a very precise control of the lancing action is needed, such as a precise control of the penetration depth, the penetration force and the duration of the lancing movement.
Further, as indicated above, a major challenge resides in the fact that the GAM-systems as described above are rather sensitive to environmental conditions and, therefore, in many cases have to be stored in sealed compartments, such as in the system described by WO 03/088834 A1. Before initiating the lancing motion, these compartment seal barriers have to be opened by some mechanism to avoid contact between the lancing system and the compartment seal barriers. This is necessary since the lancing systems for use in GAM-systems in many cases make use of hydrophilic surfaces in order to collect body fluid. These hydrophilic surfaces, however, may deteriorate and lose part of their hydrophilic properties if they come into contact with the seal barriers. Thus, in many cases, a very complicated actuating mechanism will have to be used, which, on the one hand, allows for opening of the compartments of the test element to be used, and which, on the other hand, allows for a simple initiation of the lancing motion.
WO 2006/013045 A1 discloses a blood collection system for collecting blood for diagnostic purposes. The system comprises an electric motor, which provides energy for propelling a lancet. The blood collection system also comprises a mechanical energy accumulator, in which the electric energy that is converted by the motor is stored in the form of mechanical energy. WO 2006/013045 A1 further discloses the use of a motor for biasing a spring element. The motor current is monitored in order to monitor the compression status of the spring element, and as soon as the compression of the spring element reaches a defined state, the motor is stopped, and the spring element may be released by a separate action, in order to release the mechanical energy and in order to start the lancing motion.
WO 2007/006399 A1 discloses a lancet device by means of which a lancet can be displaced along a puncturing path in order to create a puncture wound on a skin surface, especially to obtain body fluid for diagnostic purposes. The lancet device comprises a lancet drive with a driving means generating a driving force for a puncturing movement of the lancet along the puncturing path in the direction of the skin surface. The lancet drive is provided with a magnet, with the aid of which a magnetic retaining force can be generated that acts counter to the driving force, as well as triggering means which allow the retaining force to be reduced such that the lancet is accelerated in the direction of the skin surface under the effect of the driving force generated by the driving means.
The systems disclosed by WO 2006/013045 A1 and by WO 2007/006399 A1 provide a significant improvement with regard to the control of the lancing motion. Nevertheless, both in the system disclosed by WO 2006/013045 A1 and in the system disclosed in WO 2007/006399 A1, an active triggering mechanism for triggering the lancing motion is required, which in some cases might increase the complexity of the system. Further, a precise control of the penetration depth of the lancing motion remains a challenge.
Therefore, there is a need for a simple and environmentally protected system that allows for a very precise control of the lancing motion of a lancet as well as for a precise depth control of the sampling of body fluid.